1. Field of the Invention
The present invention relates generally to computer generated graphics. More particularly, the present invention relates to shading for three-dimensional computer generated graphics.
2. Background Art
Providing aesthetically pleasing visual results for three-dimensional computer generated graphics is an important and challenging task. As entertainment media such as movies and video games increasingly rely on three-dimensional computer generated graphics to supplement or replace live action footage or traditional painting techniques, it becomes important to streamline the computer aided workflow process. By providing artists and other creative professionals with intuitive computer based tools that ease the transition from ideas to computer generated renderings, visually appealing three-dimensional graphics can be more easily integrated into creative media while adhering to project budgets and schedules.
In particular, most three-dimensional characters, such as humans or animals, will have some kind of hair or fur on their bodies needing to be rendered. Human vision is very sensitive to the appearance of hair and can detect subtle inaccuracies in its appearance. Moreover, since hair can provide a very personal expression of style and creativity, hair is often considered one of the most important customization features for avatars, such as for online social communities and gaming networks. Thus, the importance of providing aesthetically pleasing hair is not to be overlooked.
On the other hand, rendering hair is not a trivial matter as it is computationally expensive to model the complex behavior of light scattering events in a volume of hair. While there has been much research on hair shading using physical models, it is difficult for computer graphics rendering to benefit from such research. Since the rendering parameters are based on physical material properties such as indices of refraction and absorption coefficients, it is difficult for artists and other creative professionals to manipulate the rendering parameters to achieve a specific aesthetic goal. In particular, due to the laws of physics and the coupling of physical material properties to multiple visual effects, it is difficult to create specific aesthetic changes, such as adjusting only the width of hair highlights, without changing the appearance of the rendering as a whole.
Thus, while physically based shading models can provide realistic and aesthetically pleasing results, they are often inappropriate for creative works due to their unintuitive art direction behavior. As a result, ad-hoc shaders that are more easily manipulated by artists have become common in production use. However, such ad-hoc shaders may lack the richness of detail provided by physical shaders, thereby providing a sub-optimal aesthetic appearance that may also break down in certain lighting conditions.
Accordingly, there is a need to overcome the drawbacks and deficiencies in the art by providing a three-dimensional computer graphics rendering system capable of producing aesthetically pleasing results for features such as hair while providing intuitive manipulation controls for art direction.